Photomultiplier Tubes camera build

[gary]

Perhaps with smaller holes PMT might have to work at higher voltage but yes i will have to do better next time i make one .I think with the light i have and if i had the right size holes it might be to dim for my eyes as a monitor ...but interesting how far out i am .

Well, that may be so, but that is the problem with physics - it isn't optional, you have to take it as it comes.

You can have lower sensitivity (lower voltage) and more light (greater aperture size), but it will always be at the expense of something else - in this case resolution, that is, the ability to resolve detail.

It boils down to this, if you want a crisp sharp picture you need an aperture size that is proportional to the diameter of the disk, the number of lines, and the aspect ratio of the picture - PI times diameter divided by the number of lines times the aspect ratio.

In the case of your sized disk (120mm) this is a maximum of (PI * 120) / (32 * 1.5) = 0.24 mm.

In truth, because the the picture is curved and not rectangular we calculate from the middle of the picture not the outside edge and that gives .223 mm

That's the dimension across a rectangular (optimum) aperture but because we use circular (sub-optimum) we tend to make them a bit bigger so that there is some overlap.

[Harry Dalek]

Yes Gary i see the problem well i will try and do better on the next nipkow,being way off here i can only do better ...i will use the microscope on the next tries .

The microscope was not great on the video side for this may be because i had to get to close

This below is about the best from the 2 different cameras ...btw tried the lens in front that didn't work well worth a shot .

[gary]

Harry, given the problems you obviously have in getting a stable picture, from what I can see the quality of the disk is within what one could expect from a home made disk of this size, at least in terms of aperture position. It would, of course, be great to get a few frames that weren't rolling but you can only do what you can do.

[Harry Dalek]

Harry, given the problems you obviously have in getting a stable picture, from what I can see the quality of the disk is within what one could expect from a home made disk of this size, at least in terms of aperture position. It would, of course, be great to get a few frames that weren't rolling but you can only do what you can do.

Yes Gary
It wasn't really made for this does but show me in some ways does a better job used in the camera but i can see the wavy look to lines on the camera must be an electronic problem...when i make the next one i would expect the hole will be tiny compared to this one .
It was good to see it as a monitor .. never thought of using it as one for testing the disk ...
Need to get back to that motor control causing problems here bad enough.

[gary]

Harry, given the problems you obviously have in getting a stable picture, from what I can see the quality of the disk is within what one could expect from a home made disk of this size, at least in terms of aperture position. It would, of course, be great to get a few frames that weren't rolling but you can only do what you can do.

Yes Gary
It wasn't really made for this does but show me in some ways does a better job used in the camera but i can see the wavy look to lines on the camera must be an electronic problem...when i make the next one i would expect the hole will be tiny compared to this one .
It was good to see it as a monitor .. never thought of using it as one for testing the disk ...
Need to get back to that motor control causing problems here bad enough.

Well don't forget you can use the monitor mode to test the motor control

[Harry Dalek]

Well don't forget you can use the monitor mode to test the motor control

OK i will leave the monitor and work on this ,had no time yesterday may this afternoon/

[Harry Dalek]

Hi Gary i got out to the shed and my dual scope adjusted the pulse width to the opto sine wave as you showed me on page 18 ,i took some short screen shots which i will add here later so check later in the day .
I also readjusted the opto reflector as i was getting a bit of a dip every now again same spot ...now all same amplitude or best it gives i can see a very slight disk wobble and i think its coming up a touch in the sine wave .
After your adjustment idea its start up to wanted speed looks good and stays on 400 hz with a 1 hz 399 400 look on my frequency meter ....now this is good i was ready to try and change my mosfet today so the old irf630n lives another day

Looking at the video it should just bounce a touch but at times it still rolls a bit and i was wondering as it shouldn't is this due to we are not using the sync from the video its just free running independently of the motor control no syncing between the 2 apart from they are at the same frequency ..i see the loop play back for video on vlc player i use when the video stops and restarts it knocks it out ..also changing video pictures which is the editing i suppose.

[gary]

Hi Gary i got out to the shed and my dual scope adjusted the pulse width to the opto sine wave as you showed me on page 18 ,i took some short screen shots which i will add here later so check later in the day .
I also readjusted the opto reflector as i was getting a bit of a dip every now again same spot ...now all same amplitude or best it gives i can see a very slight disk wobble and i think its coming up a touch in the sine wave .
After your adjustment idea its start up to wanted speed looks good and stays on 400 hz with a 1 hz 399 400 look on my frequency meter ....now this is good i was ready to try and change my mosfet today so the old irf630n lives another day

Looking at the video it should just bounce a touch but at times it still rolls a bit and i was wondering as it shouldn't is this due to we are not using the sync from the video its just free running independently of the motor control no syncing between the 2 apart from they are at the same frequency ..i see the loop play back for video on vlc player i use when the video stops and restarts it knocks it out ..also changing video pictures which is the editing i suppose.

Yes Harry that roll would be the variation in xtal frequencies we talked about earlier - theoretically you should be able to "tweak" the roll out with the xtal trim cap - but it may be too sensitive to get it perfect.

Harry I am not sure I follow you with the vlc player - I assume you mean when the video gets to the end and loops back to the start you get a break in the display - that's understandable but if by "knocks it out" you mean you lose sync then that shouldn't happen - you will lose framing due to the time gap between end and restart however.

It sounds like you have improved the encoder syncs Harry so it will be interesting to see if it fixes up the wavy syncs. You wouldn't need to go back into camera mode to see that - just recorder whatever is coming out of the sync mixer.

[Harry Dalek]

Yes Harry that roll would be the variation in xtal frequencies we talked about earlier - theoretically you should be able to "tweak" the roll out with the xtal trim cap - but it may be too sensitive to get it perfect.

OK Gary i am a bit iffy on adjusting that again as it is seems ok for the camera now and i don't have an accurate enough frequency meter ..Yes close enough good enough

Harry I am not sure I follow you with the vlc player - I assume you mean when the video gets to the end and loops back to the start you get a break in the display - that's understandable but if by "knocks it out" you mean you lose sync then that shouldn't happen - you will lose framing due to the time gap between end and restart however.

i am not sure if it would if i used the video sync but its expected signal stops and starts again ,may be its just pot luck when the video plays it syncs correct and rolls all in the same places may be in the editing ..i think i got a good enough video of it i will post up

It sounds like you have improved the encoder syncs Harry so it will be interesting to see if it fixes up the wavy syncs. You wouldn't need to go back into camera mode to see that - just recorder whatever is coming out of the sync mixer.

OK will do have to hook up the 555 to the video sync mixer it was still disconnected from last time
The scope is the out of the lm311 and 555 lined up the 555 pulse width it was a touch wide before .

BTW i noticed some printers i have scrapped come with a clear encoder and what looks like a line around the edge are bars in micro distance i might be able to use this for testing nipkow holes in the future .

[gary]

OK Gary i am a bit iffy on adjusting that again as it is seems ok for the camera now and i don't have an accurate enough frequency meter ..Yes close enough good enough

I am not sure why you would want to use a frequency meter Harry, just tweak it until the picture stops rolling.

Edit: (Remember how you used to do it with old CRT TVs with the vertical hold to stop the picture rolling? Same thing really)

[Harry Dalek]

I am not sure why you would want to use a frequency meter Harry, just tweak it until the picture stops rolling.

OK i was at first seeing if the motor control via the lm317 current controller was off to the mosfet but it was controlling ..i see your point use your eyes

[Harry Dalek]

I have to explain a problem i just found and i am not sure why ....
Has to do with the motor control ....Now i watch the motor speed by connecting a probe to the output of the opto reflector trany and the probe has a 100k resistor or the signal is to high for my laptop viewing the speed on the sound card scope program .

When i have the probe connected at this test point motor speed is near on perfect

S1 wav

S2 is start up to correct speed again with probe connected .

s2connectsyncmixer.wav shows how frequency then starts to drifts


s4disconnectingprobe.wav disconnecting the probe and it also drifts

So what i am seeing is if i don;t have that probe connected to that opto test point the motor control stops working correctly ....i wonder if its effecting the resistance of the trimmer on the opto trany as i set the correct speed setting with the probe in place here ....very annoying

Testing the speed on either the video sync mixer or the 555 its still out it stops motor controlling and drifts very strange .

[Harry Dalek]

Looked into the printer encoder ...i am not sure how tiny these encoders can get ..but its a way to measure below a 1 mm

[gary]

I have to explain a problem i just found and i am not sure why ....
Has to do with the motor control ....Now i watch the motor speed by connecting a probe to the output of the opto reflector trany and the probe has a 100k resistor or the signal is to high for my laptop viewing the speed on the sound card scope program .

When i have the probe connected at this test point motor speed is near on perfect

S1 wav

S2 is start up to correct speed again with probe connected .

s2connectsyncmixer.wav shows how frequency then starts to drifts


s4disconnectingprobe.wav disconnecting the probe and it also drifts

So what i am seeing is if i don;t have that probe connected to that opto test point the motor control stops working correctly ....i wonder if its effecting the resistance of the trimmer on the opto trany as i set the correct speed setting with the probe in place here ....very annoying

Testing the speed on either the video sync mixer or the 555 its still out it stops motor controlling and drifts very strange .

Sorry for the late reply Harry - the forum has stopped sending me notifications for some reason.

Harry do you have the probe's ground lead connected to the signal ground when you do that? You should.

[Harry Dalek]

Sorry for the late reply Harry - the forum has stopped sending me notifications for some reason.

Harry do you have the probe's ground lead connected to the signal ground when you do that? You should.

HI Gary
Yes pretty much ...i will test make sure every thing is grounded just in case .

I have just been thinking about the problem since i found out its doing this ...i am thinking of testing the resistance of of the probe to ground as its connected to the computer as see what its giving .

For some reason the circuit works correctly when its connected and not when it isn't ...its across the opto transistors emitter pin 3 of the lm311 and ground ..when connected the motor locks great disconnect drifting starts right away and its no better than manual control .\

i have been pretty busy has no time to check whats going on ,i will look into it tonight i want to fix this once and for all .